Single piece casting of reactive alloys

ABSTRACT

A method of vacuum induction melting a charge of material includes preheating a mold; inserting the charge into the mold; placing the mold into a chamber; reducing an operating pressure within the chamber; induction melting the charge within the mold; allowing material of the charge to fill a cavity defined within the mold; applying electromagnetic pressure to the charge within the mold; and applying an electromagnetic field to material of the charge positioned within the cavity defined within the mold.

1. CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of U.S.Provisional Patent Application No. 61/635,963, attorney docket no.FSPT.00001, filed on Apr. 20, 2012, the disclosure of which isincorporated herein by reference.

This application claims the benefit of the filing date of U.S.Provisional Patent Application No. 61/651,620 attorney docket no.FSPT.00002, filed on May 25, 2012, the disclosure of which isincorporated herein by reference

2. BACKGROUND

This disclosure relates to systems for investment casting parts usingmaterials that are heated to a molten state using an induction heatingsystem to permit the materials to then fill a mold that defines one ormore cavities for defining the shape of a finished part.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a and 1 b are flow chart illustrations of an exemplary systemfor induction melting.

FIG. 2 a is an illustration of an exemplary embodiment of a mold havinga cup and defining one or more cavities in communication with the cup.

FIG. 2 b is an illustration of an exemplary embodiment of the mold ofFIG. 2 a having a reactive charge of material positioned within the cupof the mold.

FIG. 2 c is an illustration of the mold of FIG. 2 b positioned within aschamber having an induction heating coil.

FIG. 2 d is a graphical illustration of an exemplary embodiment of athermal profile of a charge of material during operation of the methodof FIGS. 1 a and 1 b.

FIG. 3 a is a photograph of an exemplary experimental embodiment of themicrostructure of the blade of a turbine wheel provided using the methodof FIGS. 1 a and 1 b.

FIG. 3 b is a photograph of an exemplary experimental embodiment of themicrostructure of the blade root of a turbine wheel provided using themethod of FIGS. 1 a and 1 b.

FIG. 3 c is a photograph of an exemplary experimental embodiment of themicrostructure of the hub of a turbine wheel provided using the methodof FIGS. 1 a and 1 b.

FIG. 4 a is a photograph of an exemplary experimental embodiment of themicrostructure of the blade root of a turbine wheel provided using themethod of FIGS. 1 a and 1 b.

FIG. 5 a is a photograph of an exemplary experimental embodiment of acasting of a turbine wheel generated using the method of FIGS. 1 a and 1b.

FIG. 5 b is a photograph of an exemplary experimental embodiment of acasting of a turbine wheel generated using a VAR method of casting.

FIG. 6 a is a photograph of a cross section of an exemplary experimentalembodiment of a casting of a turbine wheel generated using the method ofFIGS. 1 a and 1 b.

FIG. 6 b is a photograph of a cross section of a casting of a turbinewheel generated using a VAR method of casting.

FIG. 7 a is a photomicrograph of a cross section of an exemplaryexperimental embodiment of a casting of a turbine wheel generated usingthe method of FIGS. 1 a and 1 b.

FIG. 7 b is a photomicrograph of a cross section of a casting of aturbine wheel generated using a VAR method of casting.

DETAILED DESCRIPTION

In the drawings and description that follows, like parts are markedthroughout the specification and drawings with the same referencenumerals, respectively. The drawings are not necessarily to scale.Certain features of the invention may be shown exaggerated in scale orin somewhat schematic form and some details of conventional elements maynot be shown in the interest of clarity and conciseness. The presentinvention is susceptible to embodiments of different forms. Specificembodiments are described in detail and are shown in the drawings, withthe understanding that the present disclosure is to be considered anexemplification of the principles of the invention, and is not intendedto limit the invention to that illustrated and described herein. It isto be fully recognized that the different teachings of the embodimentsdiscussed below may be employed separately or in any suitablecombination to produce desired results. The various characteristicsmentioned above, as well as other features and characteristics describedin more detail below, will be readily apparent to those skilled in theart upon reading the following detailed description of the embodiments,and by referring to the accompanying drawings.

Referring to FIGS. 1 a and 1 b, an exemplary embodiment of a method 100for induction melting of titanium aluminide includes, in 102, providinga conventional ceramic mold having a cup in communication with a cavitydefined within the mold for defining a shape of a part.

Referring to FIG. 2 a, in an exemplary embodiment, 102, the mold 102 aincludes a cup 102 b in communication with a cavity 102 c defined withinthe mold for defining a shape of a part. As will be recognized bypersons having ordinary skill in the art, the cavity 102 c definedwithin the ceramic mold 102 a may define one or more cavities permittingmolten materials to fill therein and thereby define the shape of a part.In an exemplary embodiment, the cavity 102 c of the mold 102 a defines aturbine or a compressor wheel.

Referring again to FIGS. 1 a and 1 b, in an exemplary embodiment areactive alloy charge is then provided in a conventional manner in 104.In an exemplary embodiment, the reactive alloy charge comprises areactive alloy such as, for example, a titanium alloy which may, forexample, be titanium aluminide.

Then, in 106, in an exemplary embodiment, the mold 102 a may bepreheated in a conventional manner.

Then, in 108, in an exemplary embodiment, referring to FIGS. 1 a, 1 band 2 b, the reactive alloy charge 108 a is then placed within the cup102 b of the preheated mold 102 a in a conventional manner, in 108. Inan exemplary embodiment, before, during or after preheating the mold in106, the charge 108 a may also be preheated.

Then, in 110, in an exemplary embodiment, referring to FIGS. 1 a, 1 b,and 2 c, the mold 102 a is placed into a conventional chamber 110 ahaving a conventional high frequency alternating current inductionheating coil 110 b such that the mold 102 a is surrounded by the coil ina conventional manner. In an exemplary embodiment, chamber 110 acomprises a quartz chamber.

Then, in 112, in an exemplary embodiment, the operating pressure withinthe chamber 110 a is reduced in a conventional manner. In an exemplaryembodiment, in 112, the operating pressure within the chamber 110 a isreduced to less than about 100 millitorr.

Then, in 114, in an exemplary embodiment, the induction coil 110 b isoperated, in a conventional manner, to apply a time dependentelectromagnetic field to mold 102 a. In an exemplary embodiment, as willbe recognized by persons having ordinary skill in the art, the operationof the induction coil 110 b to apply a time dependent electromagneticfield to mold 102 a will thereby induce eddy currents within thereactive alloy charge 108 a thereby heating, and eventually melting andrendering molten, the reactive alloy charge. Furthermore, as will berecognized by persons having ordinary skill in the art, the operation ofthe induction coil 110 b to apply a time dependent electromagnetic fieldto mold 102 a will thereby also generate an electromagnetic field whichis opposed to the applied time dependent electromagnetic field andcreating repulsive pressures on the reactive alloy charge 108 a.

In an exemplary embodiment, during the operation of the method 100, theapplication of the time dependent electromagnetic field in 114 isprovided in multiple stages in which the intensity of the time dependentelectromagnetic field is increased. For example, as illustrated in FIG.2 d, in an exemplary embodiment, the application of the time dependentelectromagnetic field in 114 is provided such that the operatingtemperature of the charge 108 a is increased in multiple stages untilmelting of the charge 108 a is completed. Then, the intensity of thetime dependent electromagnetic field is continually decreased followingcomplete melting of charge 108 a.

Then, in an exemplary embodiment, in 116, the induction coil 110 b isoperated to manipulate the time dependent applied electromagnetic fieldto apply greater magnetic pressure on a top portion of the reactivealloy charge 108 a relative to a bottom portion of the reactive alloycharge. The general manner of manipulating a time dependent appliedelectromagnetic field to apply different magnetic pressures at differentlocations is considered well known in the art. For example, manipulatinga time dependent applied electromagnetic field to apply differentmagnetic pressures at different locations, may be provided by using anon-constant diameter induction coil, or providing an additionalinduction coil disposed around a portion of the first induction coil.

In an exemplary, in 116, the application of a greater magnetic pressureto the a top portion of the reactive alloy charge 108 a relative to thebottom portion of the reactive alloy charge acts to apply a force to thecharge that injects the charge into the cavity 102 c of the mold 102 a.

Then, in 118, the operations of 114 and 116 are then continued until thereactive charge 108 a is completely melted and injected into the cavity102 c of the mold 102 a by operation of the induction coil 110 b.

In an exemplary embodiment, during the operation of the method 100,initially, the upper portion of the charge 108 a is melted first, due tothe greater electromagnetic field applied to that portion of the charge.Then, in an exemplary embodiment, during the operation of the method100, the melting of the upper portion of the charge 108 a is thenfollowed by melting of the bottom portion of the charge due to acombination of electromagnetic induced heating and convection. In anexemplary embodiment, during the operation of the method 100, themelting of the bottom portion of the charge 108 a is then followed bythe injection of the melted portion of the charge 108 a due to theapplication of the magnetic pressures onto the charge 108 a in 116.Thus, it is important to maintain a seal between the cup 102 b and thecavity 102 c until the charge 108 a is completely melted.

As will be recognized by persons having ordinary skill in the art, theoperation of the induction coil 110 b in 114 will alsoelectromagnetically stir the melted portion of the reactive alloy charge108 a.

In an exemplary embodiment, operation of the induction coil 110 b in 114will also apply an electromagnetic field to the melted and/or solidifiedportions of the reactive alloy charge within the cavity 102 c of themold 102 a. As a result, filling of the cavity 102 c of the mold 102 ais improved, thereby permitting thinner parts to be formed and defectsmay be contained and limited to an off part, or non-critical, section.Furthermore, in an exemplary embodiment, application of anelectromagnetic field to the melted and/or solidified portions of thereactive alloy charge 108 a within the cavity 102 c of the mold 102 apermits controlling and modifying a structure of the solidified portionof the reactive alloy 108 a within the cavity 102 c of the mold 102 a.Furthermore, in an exemplary embodiment, application of anelectromagnetic field to the melted and/or solidified portions of thereactive alloy charge 108 a within the cavity 102 c of the mold 102 apermits the portion of the reactive alloy charge 108 a within the cavity102 c of the mold 102 a to remain controllably molten such that theoperator may control and determine which portion of the reactive alloycharge 108 a within the cavity 102 c of the mold 102 a is the lastportion to solidify.

In several exemplary embodiments, one or more elements of the mold 102 amay be fabricated from a graphite material. For example, in an exemplaryembodiment, the mold 102 a may include a graphite cup 102 b and/or agraphite cup liner. Furthermore, in an exemplary embodiment, at least aportion of the mold 102 a that defines the cavity 102 c may also includea graphite material. In an exemplary embodiment, where at least portionsof the mold 102 a include a graphite material, since graphite can be anelectrical conductor, during operation of the method 100, the graphiteportions of the mold 102 a are inductively heated thereby and provideadditional heating of the casting of the reactive alloy charge withinthe cup 102 b and/or cavity 102 c.

In several exemplary experimental embodiments of the method 100,castings of turbine wheels were provided using a reactive titanium alloycharges having the following nominal compositions: 1) titanium with 28%by weight aluminum, 9% by weight niobium, and 2% by weight molybdenum,2) titanium with 33% by weight aluminum, 5% by weight niobium and 2% byweight chromium, and 3) titanium with 6% by weight aluminum and 4% byweight vanadium.

In some exemplary experimental embodiments, the following results wereobserved: 1) there was no centerline shrinkage; 2) the macrostructurewas a symmetric and columnar solidification structure; and 3) usingconventional x-ray testing, there was no detectable gas porosity orinclusions.

Referring to FIG. 3 a, in the exemplary experimental embodiment, themicrostructure of the blade of the turbine wheel was lamellar gammatitanium aluminide with generally uniform grain and lamellae size.

Referring to FIG. 3 b, in the exemplary experimental embodiment, themicrostructure of the blade root of the turbine wheel was lamellar gammatitanium aluminide with uniform grain & lamellae sizes which wereconsistent with those of the blade microstructure.

Referring to FIG. 3 c, in the exemplary experimental embodiment, themicrostructure of the hub of the turbine wheel was lamellar gammatitanium aluminide with slightly larger grain and lamellae sizes thanfound at the root and blade.

Referring to FIG. 4 a, in the exemplary experimental embodiment, themicrostructure of the blade root of the turbine wheel was lamellar gammatitanium aluminide with generally uniform grain and lamellae size.

In several exemplary experimental comparative embodiments, the operationand results of the method 100 was compared with operation and results ofa conventional vacuum arc remelting (“VAR”) investment casting process.In all of these exemplary comparative embodiments, the investment castarticle was a compressor wheel.

In the exemplary experimental embodiments of the methods 100 and VAR,the final dimensions of the cast compressor wheels were withinacceptable manufacturing tolerances for both processes.

As illustrated in FIG. 5 a, the gating ratio for the exemplaryexperimental embodiments of the method 100 was 1.5:1. As will berecognized by persons having ordinary skill in the art, the gating ratiois equal to the ratio of the mass of the charge to the mass of theresulting cast part. The lower the gating the ratio, the more efficientthe casting process.

As illustrated in FIG. 5 b, the gating ratio for the exemplaryexperimental embodiments of the method VAR was 3.35:1.

A tabular summary of the mechanical properties of investment castturbine wheels provided by the exemplary experimental embodiments of themethods 100 and VAR is provided below:

Ultimate Tensile Yield Strength Specimen Strength (Ksi) @0.2% Offset(Ksi) Method 100 - No. 1 145.8 133.0 Method 100 - No. 2 143.4 133.6 VARAverage* 137.4 126.2

As illustrated in FIG. 6 a, exemplary experimental embodiments of themethod 100 included centerline shrinkage.

As illustrated in FIG. 6 b, exemplary experimental embodiments of themethod VAR included centerline shrinkage.

As illustrated in FIG. 7 a, exemplary experimental embodiments of themethod 100 exhibited the illustrated microstructure at 50×magnification.

As illustrated in FIG. 7 b, exemplary experimental embodiments of themethod VAR exhibited the illustrated microstructure at 50×magnification.

The results of the comparative exemplary experimental embodiments of themethods 100 and VAR demonstrated that the method 100 was and is capableof producing parts virtually identical to those provided using theconventional VAR process on every level, and in some cases the method100 produces better results than the method VAR. This was an unexpectedresult. For example, with respect to the dimensional and chemicalresults, the methods 100 and VAR processes produce similar parts. Alldimensions and elements measured from the parts made through the method100 process were within specification and capability. As far asadvantages, for example, a major advantage of the method 100 is thecapability to reduce the gating ratio versus that required for themethod VAR. Thus, the method 100 can produce the same amount of castparts as the VAR process while using less than half the amount of metal.This was an unexpected result. Furthermore, as demonstrated by theexemplary comparative experimental results, the mechanical properties ofthe parts produced using the method 100 had a greater ultimate and yieldstrength than those produced using the method VAR. This was anunexpected result. In addition, the method 100 was also capable ofsignificantly reducing the amount of centerline shrink that is developedduring casting versus that produced by the VAR method. This was anunexpected result. Furthermore, the method 100 was capable ofcontrolling the microstructure of the cast parts by controlling thecooling rates. This is possible because of the single piece process ofthe method 100, and this result allows for uniform and consistentcooling throughout the part. Comparing the parts cast in Ti6-4, thegrains structures between the methods 100 and VAR were virtuallyidentical. Thus, the method 100 provided superior results to that forthe VAR method. A tabular summary of the results provided by the methods100 and VAR is provided below:

Method 100 VAR Dimensions In Spec. and Comparable Chemistry In Spec.,Capable, and Comparable Gating Ratio 1.5:1 3.35:1 Mechanical Properties^(~)144 Ksi (UTS) ^(~)137 Ksi (UTS) ^(~)133 Ksi (YS) ^(~)126 Ksi (YS)Centerline Shrink Minimal Large Ti 6-4 Microstructure In Spec. andComparable TiAl Microstructure Controllable Incapable

A method of vacuum induction melting a charge of material and casting anarticle includes preheating a mold; inserting the charge into the mold;placing the mold into a chamber; reducing an operating pressure withinthe chamber; induction melting the charge within the mold; applyingelectromagnetic pressure to the charge within the mold; allowingmaterial of the charge to fill a cavity defined within the mold; andapplying an electromagnetic field to material of the charge positionedwithin the cavity defined within the mold. In an exemplary embodiment,the charge of material is preheated. In an exemplary embodiment, themold includes a ceramic material. In an exemplary embodiment, the chargeincludes a reactive alloy. In an exemplary embodiment, the chargeincludes a titanium alloy. In an exemplary embodiment, the chargeincludes a titanium aluminide alloy. In an exemplary embodiment, thechamber includes a quartz chamber. In an exemplary embodiment, applyingmagnetic pressure includes manipulating a time dependent electromagneticfield. In an exemplary embodiment, applying magnetic pressure includesmanipulating a time dependent electromagnetic field during a melting ofthe charge. In an exemplary embodiment, applying magnetic pressureincludes manipulating a time dependent electromagnetic field during aflowing of the charge into the cavity. In an exemplary embodiment,applying magnetic pressure includes manipulating a time dependentelectromagnetic field during a solidification of the charge. In anexemplary embodiment, applying magnetic pressure includes manipulatingelectromagnetic field gradients. In an exemplary embodiment, applyingelectromagnetic pressure includes applying a stronger electromagneticfield to an upper portion of the charge than to a lower portion of thecharge. In an exemplary embodiment, applying electromagnetic pressureincludes locating the charge within a non uniform electromagnetic field.In an exemplary embodiment, the method further includes allowing thematerial of the charge to solidify within the cavity in the presence ofan applied electromagnetic field. In an exemplary embodiment, thesolidified material includes a symmetrical structure. In an exemplaryembodiment, the solidified material includes an asymmetrical structure.In an exemplary embodiment, the solidified material does not includedetectable gas porosity using conventional gas porosity detectionmethods. In an exemplary embodiment, the solidified material does notinclude inclusions using conventional inclusion detection methods. In anexemplary embodiment, the solidified material includes a fully lamellarmicrostructure. In an exemplary embodiment, the material includestitanium aluminide. In an exemplary embodiment, the solidified materialincludes a hub and one or more blades that extend in a radial directionfrom the hub. In an exemplary embodiment, the solidified materialincludes a turbine wheel. In an exemplary embodiment, the solidifiedmaterial includes a compressor wheel.

A system for vacuum induction melting a charge of material and castingan article includes means for preheating a mold; means for inserting thecharge into the mold; means for placing the mold into a chamber; meansfor reducing an operating pressure within the chamber; means forinduction melting the charge within the mold; means for allowingmaterial of the charge to fill a cavity defined within the mold; meansfor applying electromagnetic pressure to the charge within the mold; andmeans for applying an electromagnetic field to material of the chargepositioned within the cavity defined within the mold. In an exemplaryembodiment, the system includes means for preheating the charge ofmaterial. In an exemplary embodiment, the mold includes a ceramicmaterial. In an exemplary embodiment, the charge includes a reactivealloy. In an exemplary embodiment, the charge includes a titanium alloy.In an exemplary embodiment, the charge includes a titanium aluminidealloy. In an exemplary embodiment, the chamber includes a quartzchamber. In an exemplary embodiment, the means for applying magneticpressure includes means for manipulating a time dependentelectromagnetic field. In an exemplary embodiment, the means forapplying magnetic pressure includes means for manipulating a timedependent electromagnetic field during a melting of the charge. In anexemplary embodiment, the means for applying magnetic pressure includesmeans for manipulating a time dependent electromagnetic field during aflowing of the charge into the cavity. In an exemplary embodiment, themeans for applying magnetic pressure includes means for manipulating atime dependent electromagnetic field during a solidification of thecharge. In an exemplary embodiment, the means for applying magneticpressure includes means for manipulating electromagnetic fieldgradients. In an exemplary embodiment, the means for applyingelectromagnetic pressure includes means for applying a strongerelectromagnetic field to an upper portion of the charge than to a lowerportion of the charge. In an exemplary embodiment, the means forapplying electromagnetic pressure includes means for locating the chargewithin a non uniform electromagnetic field. In an exemplary embodiment,the system further includes: means for allowing the material of thecharge to solidify within the cavity in the presence of an appliedelectromagnetic field. In an exemplary embodiment, the solidifiedmaterial includes a symmetrical structure. In an exemplary embodiment,the solidified material includes an asymmetrical structure. In anexemplary embodiment, the solidified material does not includedetectable gas porosity using conventional gas porosity detectionmethods. In an exemplary embodiment, the solidified material does notinclude inclusions using conventional inclusion detection methods. In anexemplary embodiment, the solidified material comprises a fully lamellarmicrostructure. In an exemplary embodiment, the material comprisestitanium aluminide. In an exemplary embodiment, the solidified materialincludes a hub and one or more blades that extend in a radial directionfrom the hub. In an exemplary embodiment, the solidified materialincludes a turbine wheel. In an exemplary embodiment, the solidifiedmaterial includes a compressor wheel.

A method for vacuum induction melting a charge of material and castingan article includes providing a ceramic mold which comprises a cup whichcommunicates with a cavity defined within the mold for defining a shapeof a part; providing a reactive alloy charge; preheating the mold;placing the charge of material within the preheated cup of the mold;applying a time dependent electromagnetic field to the mold; inducingelectrical eddy currents within the reactive alloy charge; generating anelectromagnetic field which is opposed to the applied time dependentelectromagnetic field and creating repulsive pressures on the reactivealloy charge; manipulating the time dependent applied electromagneticfield and applying greater magnetic pressure on a top portion of thereactive alloy charge relative to a bottom portion of the reactive alloycharge; melting at least a portion of the reactive alloy charge;electromagnetically stirring the melted portion of the reactive alloycharge; forcing the melted portion of the reactive alloy charge into atleast a portion of the cavity of the mold using the magnetic pressures;and applying an electromagnetic field to the melted portion of thereactive alloy charge within the cavity of the mold. In an exemplaryembodiment, the method includes preheating the charge of material. In anexemplary embodiment, the method further includes allowing the meltedportion of the reactive alloy charge to solidify within the cavity ofthe mold. In an exemplary embodiment, the method further includesapplying an electromagnetic field to the solidified portion of thereactive alloy charge within the cavity of the mold. In an exemplaryembodiment, the method further includes controlling and modifying astructure of the solidified portion of the reactive alloy within thecavity of the mold. In an exemplary embodiment, applying theelectromagnetic field to the solidified portion of the reactive alloycharge within the cavity of the mold includes heating treating thesolidified portion of the reactive alloy within the cavity of the mold.

A system for vacuum induction melting a charge of material and castingan article includes means for providing a ceramic mold which comprises acup which communicates with a cavity defined within the mold fordefining a shape of a part; means for providing a reactive alloy charge;means for preheating the mold; means for placing the charge of materialwithin the preheated cup of the mold; means for applying a timedependent electromagnetic field to the mold; means for inducingelectrical eddy currents within the reactive alloy charge; means forgenerating an electromagnetic field which is opposed to the applied timedependent electromagnetic field and means for creating repulsivepressures on the reactive alloy charge; means for manipulating the timedependent applied electromagnetic field and means for applying greatermagnetic pressure on a top portion of the reactive alloy charge relativeto a bottom portion of the reactive alloy charge; means for melting atleast a portion of the reactive alloy charge; means forelectromagnetically stirring the melted portion of the reactive alloycharge; means for forcing the melted portion of the reactive alloycharge into at least a portion of the cavity of the mold using themagnetic pressures; and means for applying an electromagnetic field tothe melted portion of the reactive alloy charge within the cavity of themold. In an exemplary embodiment, the system further includes means forallowing the melted portion of the reactive alloy charge to solidifywithin the cavity of the mold. In an exemplary embodiment, the systemfurther includes means for applying an electromagnetic field to thesolidified portion of the reactive alloy charge within the cavity of themold. In an exemplary embodiment, the system further includes means forcontrolling and modifying a structure of the solidified portion of thereactive alloy within the cavity of the mold. In an exemplaryembodiment, the means for applying the electromagnetic field to thesolidified portion of the reactive alloy charge within the cavity of themold includes means for heating treating the solidified portion of thereactive alloy within the cavity of the mold.

It is understood that variations may be made in the above withoutdeparting from the scope of the invention. While specific embodimentshave been shown and described, modifications can be made by one skilledin the art without departing from the spirit or teaching of thisinvention. The embodiments as described are exemplary only and are notlimiting. Many variations and modifications are possible and are withinthe scope of the invention. Furthermore, one or more elements of theexemplary embodiments may be omitted, combined with, or substituted for,in whole or in part, one or more elements of one or more of the otherexemplary embodiments. Accordingly, the scope of protection is notlimited to the embodiments described, but is only limited by the claimsthat follow, the scope of which shall include all equivalents of thesubject matter of the claims.

1. A method of vacuum induction melting a charge of material and castingan article, comprising: preheating a mold; inserting the charge into themold; placing the mold into a chamber; reducing an operating pressurewithin the chamber; induction melting the charge within the mold;applying electromagnetic pressure to the charge within the mold;allowing material of the charge to fill a cavity defined within the moldto form the article; and applying an electromagnetic field to materialof the charge positioned within the cavity defined within the mold. 2.The method of claim 1, further comprising preheating the charge.
 3. Themethod of claim 1, wherein the mold comprises a ceramic material.
 4. Themethod of claim 1, wherein the mold comprises a graphite material. 5.The method of claim 1, wherein the mold comprises a ceramic and agraphite material.
 6. The method of claim 1, wherein the chargecomprises a reactive alloy.
 7. The method of claim 6, wherein the chargecomprises a titanium alloy.
 8. The method of claim 6, wherein the chargecomprises a titanium aluminide alloy.
 9. The method of claim 1, whereinthe chamber comprises a quartz chamber.
 10. The method of claim 1,wherein applying magnetic pressure comprises manipulating a timedependent electromagnetic field.
 11. The method of claim 10, whereinapplying magnetic pressure comprises manipulating a time dependentelectromagnetic field during a melting of the charge.
 12. The method ofclaim 10, wherein applying magnetic pressure comprises manipulating atime dependent electromagnetic field during a flowing of the charge intothe cavity.
 13. The method of claim 10, wherein applying magneticpressure comprises manipulating a time dependent electromagnetic fieldduring a solidification of the charge.
 14. The method of claim 1,wherein applying magnetic pressure comprises manipulatingelectromagnetic field gradients
 15. The method of claim 1, whereinapplying electromagnetic pressure comprises applying a strongerelectromagnetic field to an upper portion of the charge than to a lowerportion of the charge.
 16. The method of claim 1, wherein applyingelectromagnetic pressure comprises locating the charge within a nonuniform electromagnetic field.
 17. The method of claim 1, furthercomprising: allowing the material of the charge to solidify within thecavity in the presence of an applied electromagnetic field
 18. Themethod of claim 17, wherein the solidified material comprises asymmetrical structure.
 19. The method of claim 17, wherein thesolidified material comprises an asymmetrical structure.
 20. The methodof claim 17, wherein the solidified material does not include detectablegas porosity using conventional gas porosity detection methods.
 21. Themethod of claim 17, wherein the solidified material does not includeinclusions using conventional inclusion detection methods.
 22. Themethod of claim 17, wherein the solidified material comprises a fullylamellar microstructure.
 23. The method of claim 22, wherein thematerial comprises a titanium aluminide alloy.
 24. The method of claim17, wherein the solidified material comprises a hub and one or moreblades that extend in a radial direction from the hub.
 25. The method ofclaim 17, wherein the solidified material comprises a turbine wheel. 26.The method of claim 17, wherein the solidified material comprises acompressor wheel.
 27. A method for vacuum induction melting a charge ofmaterial and casting an article, comprising: providing a ceramic moldwhich comprises a cup which communicates with a cavity defined withinthe mold for defining a shape of a part; providing a reactive alloycharge; preheating the mold; placing the charge of material within thepreheated cup of the mold; applying a time dependent electromagneticfield to the mold; inducing electrical eddy currents within the reactivealloy charge; generating an electromagnetic field which is opposed tothe applied time dependent electromagnetic field and creating repulsivepressures on the reactive alloy charge; manipulating the time dependentapplied electromagnetic field and applying greater magnetic pressure ona top portion of the reactive alloy charge relative to a bottom portionof the reactive alloy charge; melting at least a portion of the reactivealloy charge; electromagnetically stirring the melted portion of thereactive alloy charge; forcing the melted portion of the reactive alloycharge into at least a portion of the cavity of the mold using themagnetic pressures to form the article; and applying an electromagneticfield to the melted portion of the reactive alloy charge within thecavity of the mold.
 28. The method of claim 27, further comprisingallowing the melted portion of the reactive alloy charge to solidifywithin the cavity of the mold.
 29. The method of claim 28, furthercomprising applying an electromagnetic field to the solidified portionof the reactive alloy charge within the cavity of the mold.
 30. Themethod of claim 29, further comprising controlling and modifying astructure of the solidified portion of the reactive alloy within thecavity of the mold.
 31. The method of claim 29, wherein applying theelectromagnetic field to the solidified portion of the reactive alloycharge within the cavity of the mold comprises heat treating thesolidified portion of the reactive alloy within the cavity of the mold.